Projector electrode



Patented Dec. 19, 1922.

PATENT OFFICE.

UNITED STATES WILLIAM ROY MO'IT, OF LAKEWOOD, OHIO,.ASSIGNOR T0 NATIONAL CARBON COMPANY, INC., A CORPORATION OF NEW YORK.

PROJECTOR ELECTRODE.

No Drawing.

To all whom it may concern:

Be it known that I, WILLIAM R. Mom, a

citizen of the United States, residing at Lakewood, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Projector Electrodes, of which the following is a full, clear, and exact description.

This invention relates to projector carbons and is particularly applicable to lamps for projecting so-called moving pictures onto screens. The carbon arc is extensively used in moving picture projection on account of its high candle power and the concentration of the light in a restricted spot. For a long time direct current was the chief source of power used with projector lamps for this purpose, as it requiresa very heavy current to produce satisfactory results, and

with heavy alternating currents the are was so excessively noisy that it could hardly be endured by the operator in his booth, and

was annoying to the audience as well. Of course, alternating current lamps such as street lamps, etc., are more or less noisy, but this noise is small indeed, as compared to the terrific roar produced by a projector lamp with heavy alternating current (e. g. 60 amperes) when ordinary electrodes are used.

I have devised an alternating current electrode for projection lamps that almost entirely eliminates the noise. The addition of the materials for producing these results has no harmful effect on the light-giving properties or mechanical strength of the electrode. On the contrary, the candle power and arc steadiness is considerably increased, and the mechanical strength of the core is materially raised.

To bring about the desired results, I incorporate the fluorides of the rare-earth metals (that is, the fluorides of the metals in the well known \Velsbach residue) in the core of the carbon electrodes. Various amounts of the material may be used, and various sizes of electrodes are permissible, but, by way of example, I may state that with a five-eighths inch carbon adapted for use in a 60 ampere projector lamp. the core hole is about fifteen hundredths of an inch in diameter, and this is filled with the'following mixture by way of example 6 parts rare-earth fluorides.

4 parts ground carbon.

Application filed July 28, 1919. Serial No. 313,954.

1 part potassium silicate.

1 part'sodium silicate.

Instead of using the rare-earth mixture of the Welsbach residue, I may separate the constituents out and use each individually or in various proportions. I have found from tests of the rare-earths used singly,that the fluorides of cerium, neodymium and yttrium are best for reducing noise, though the other rare-earths such as thorium and lanthanum have a very material effect as noise reducers.

I may use the rare-earth fluorides with other binding agents but I prefer the silicates of sodium and potassium, preferably both of them. Sodium silicate seems to enhance the effect of the fluorides, but it is desirable to employ some potassium silicate since it is a most excellent arc supporter. Of course, are supporters reduce the size of the crater and diminish the candle power, but they cannot be dispensed with, particularly in alternating current projector carbons. The are supporters thusestablish the crater size and to prevent further reduction of crater size I use a low content of rareearth fluoride, or equivalent. Fortunately, small amounts of such materials reduce the noise very effectively, and the crater is not reduced to the small size of the ordinary flaming arc. Potassium silicate tends to reduce the crater brightness, While sodium silicate does not do this to so great an extent, so that a mixture of the tWo' gives a well balanced core in this respect.

I find that the rareearth fluorides should be used in relatively small quantities, or else difficulty will be encountered by the production of an arc of too high flaming characteristics. In no case should sufficient quantities be used to produce a flaming are as is found in arc lamps for general illumination. In fact, small enough quantities should be used to preclude it from reducing the size of the crater to any material extent. The

. fluorides should preferably be less than about 6% of the Weight of the rest of the carbon electrode, say from about 1% to 6%,and I have found that 4% is a good proportion to use.

In practice it will be found desirable to use the fluoride mixture in the lower electrode and to incorporate in the core of the upper a mixture of potassium silicate and the condenser lens and breakage occurs.

However, I have equally distributed the fluoride mixture in the cores of the two shells with good results,and other ratios of distribution could also be used.

My invention is not limited to any theory of operation, but my experiments have caused me to believe the following is correct Sincethe current rises from zero value vto maximum and diminishes to zero twice in each cycle, it is evident that the heat of the arc varies considerably at the same time. At the time of maximum current, that is, at thepeak of the wave, there is maximum heat and at zero value of current there is minimum heat. I believe that this variation is what *auses the noise, and in my improvement I believe I reduce the noise by supplying materials that act as a reservoir for energy to smooth out the heat curve. Rare earth compounds boil at a very high temperature and. condense into liquid form very readily on lowering of temperature. There fore, when the heat of the arc is at a maximum, the rare-earth compounds are vaporized and absorb a great amount of heat. At minimum temperature of the are they condense back again and liberate the heat again. In this way they tend to maintain the heat content of the are uniform and this I believe is why they make the arc practically noiseless.

My belief in the correctness of the theory advanced above is strengthened by the fact that my improvement also reduces the hissing of direct current arcs. The D. C. are as well as the A. (7.. contains carbon vapor and this of course burns to carbon monoxide or dioxide (depending upon circumstances) on contact with air. This of course takes place with liberation of a great amount of heat on-the outer surface of the arc stream. The sudden rise of temperature causes the carbon vapor to burn all the faster and tends to deplete the outer surface of the arc streamof carbon vapor. The temperature then drops until additional carbon vapor reaches the outer surface, when the cycle is again passed through. In this way the surges of carbon vapor causes variations'iu heat content on the outer portion of the arc-stream and a hissing noise is'produced. The rare-earth fluorides, when used in D. t. electrodes,

smooth out the heat content in a way'ex-' plained in the description of the A. C. improvement. When the electrodes of my in:

'vention are employed to reduce the hissing and otherwise improve the D. C. arc. I prefer to use the white-flame material only in the positive. I

The burning of the carbon vapor in A. C. arcs tends to accentuate the heat difl'erence,

as there is greatest burning at maximum heat content of the arc. The fluorides mentioned, however, reduce this tendency.

Regardless of the theory of operation. I have found that my improvement reduces the noise of A. C. projection arcs down to about 1 to 5% of whatit would otherwise be, and the hissing of D. C. projection arcs is likewise reduced. limited to the theory advanced.

In projection lamps the arc tends to jump from the crater to one side of the carbon electrode and back again. This .is called chasing by the trade. I have found that such chasing of the arc is due to the collection of ash on the side of the shell. The usual ash consists of the oxides of iron. aluminum and calcium, and these reduce the are resistance, so that the arc will jump to the deposit of ash on the side. where it will stay until the ash is consumed. The chasing of the arc in this way produces unsteadiness that is very annoying to observers of the projection on the screen, and its elimination is very desirable. Rare-earth fluorides r duce the resistance of the arc and by putting them in the electrode or electrodes there is no tendency for the arc to jump to an ash de-- posit on one side of the shell. My improvement therefore materially steadies the are by substantial elimination of chasing.

In the arc stream a portion of the rareearth fluorides are converted into oxides and carbides, but these. have the same effect on the noise and steadiness of the arc, and I may therefore use the oxides and oxysalts. etc., of the rare-earths in the first instance.

In addition to very effectively reducing the noise and unsteadiness. as stated, the rare-earth fluorides give a white light and materially increase the. candle power.

I, of course, am aware that rare-earth compounds have been used in arc lamps for illuminating purposes. but these have always been employed in large amounts as, compared to the amount necessary for reducing the noise in projector carbons, and no one was aware of the fact that these compounds reduced the noise of alternatingprojector carbons or decreased the hissing of D. C. arcs. This was due to the fact that the current in ordinary street lamps is small compared to that used in projector lamps and the noise of hissing was of no consequence. In such lamps the rare-earth compounds are used in such quantities as to rcduce the crater size to such an extent that the electrodes could not l)(' used as projector carbons. Also the arc would be of such flaming nature as to preclude use in projection apparatus.

Having described my invention, what I claim is:

1. A projector electrode having a core comprising rare-earth metal compound, the

weight of such compound being less than about (3% of the weight of the rest of the electrode.

A projector electrode having a core containing rare-earth metal compound, the weight of such compound being from 1% to 6% of the weight of the rest of the electrode.

A projector electrode having a core containing rare-earth metal fluoride, the weight of such fluoride being from 1% to 6% of the weight of the rest of the electrode.

4. A projector electrode having a core containing rare-earth metal compound, the weight of such compound being about of the weight of the rest of the electrode.

5. A projector electrode having a core containing rare-earth metal fluoride or fluorides and binding means comprising an arc supporter, the weight of such fioride or fluorides being not more than 4% of the weight of the rest of the electrode.

6. In a projector lamp, cooperating upperand lower electrodes having cores containmg rare-earth metal compounds, the welght of such compounds being from 1% to 6% of the weight of the rest of the electrodes.

7. For use in an alternating current projector lamp, cooperating upper and lower electrodes, said lower electrode having a core containing rare-earth metal compound, the weight of such compound being from 1% to 6% of the weight of the rest of the electrode.

8. In a projector lamp, cooperating upper and lower cored electrodes, the core of said lower electrode containing rare-earth metal compound, the weight of such compound being about 4% of the weight of the rest of the electrode.

9. In a projector lamp, cooperating upper and lower cored electrodes, the core of said lower electrode containing rare-earth metal fluoride, the weight of such fluoride being from 1% to 6% of the weight of the rest of the electrode.

In testimony whereof, I hereunto afiix my signature.

WM. ROY MOTT. 

